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ANATOMY3: Orbital contents > Extraorbital muscles > Flashcards

Extraorbital muscles Flashcards

1
Q

How many true extraocular muscles are responsible for movements of the globe?

A

six

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2
Q

In addition to the 6 intraocular muscles responsible for movements of the globe, what is 1 further orbital muscle?

A

the levator palpebrae superioris

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3
Q

What is the origin of the levator palpebrae superiororis muscle?

A

orbital apex

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4
Q

What are the insertions of the levator palpebrae superioris?

A

tarsal plate and upper eyelid

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5
Q

What are the 6 true extraocular muscles (2 groups)?

A
  • 4 rectus muscles
  • 2 oblique muscles
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6
Q

Where do the 4 rectus muscles arise?

A

tendinous ring at apex of the orbit

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7
Q

What is the insertion of the four rectus muscles?

A

insert into the sclera about 4-8mm behind the limbus

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8
Q

What are the 2 oblique muscles?

A

superior and inferior oblique muscles

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9
Q

What is the importance of the tendon length of the extraocular muscles?

A

important in the surgical management of strabismus

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10
Q

What do the collagen bundles of the tendons of the EOMs blend with?

A

the scleral collagen

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11
Q

What is shown in the diagram?

A

the orbit viewed from above, revealing relations of the orbital nerves and extraocular muscles (orbital fat and vessels excluded for clarity)

Roof of orbit and superior orbital fissure removed and periorbita divided

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12
Q

Where does the sensory root of the ciliary ganglion emerge from?

A

the nasociliary nerve

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13
Q

Where does the motor root (parasympathetic fibres) of the ciliary ganglion arise?

A

branch of the oculomotor supplying the inferior oblique

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14
Q

What is shown in the top image?

A

lateral view of a dissected orbit revealing the relations of the orbital nerves and extraocular muscles (vessels have been excluded for purposes of clarity)

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15
Q

What is shown in the image?

A

dissection of the orbit with lateral rectus uncut, course of orbital nerves within cavernous sinus shown (by removal of lateral dural wall)

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16
Q

Where is the ciliary ganglion located?

A

The ciliary ganglion lies between the lateral rectus and the optic nerve.

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17
Q

What is a useful landmark for finding the ciliary ganglion?

A

the nerve to the inferior oblique (NIO)

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18
Q

Where do the short ciliary nerves emerge and where do they enter the globe?

A

The short ciliary nerves emerge from the ciliary ganglion and enter the globe around the optic nerve

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19
Q

What are the three nerves that enter the orbit outside the tendinous ring?

A

lacrimal, frontal and trochlear

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20
Q

What is the nervous supply to the superior rectus muscle?

A

branch of superior division of III nerve

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21
Q

Which other muscle does the nerve supplying the superior rectus muscle innervate and how does it reach it?

A

pierces the muscle and enters the levator palpebrae superioris, which it supplies, from below

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22
Q

Where do branches of the pterygopalatine ganglion (PTG) enter the orbit to contribute to the formation of the retrobulbar plexus?

A

enter the orbit through the inferior orbital fissure

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23
Q

What plexus do branches of the PTG supply?

A

contribute to the formation of the retrobulbar plexus (not shown)

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24
Q

Where does the inferior oblique muscle pass in relation to the inferior rectus?

A

Inferior oblique passes backwards, laterally and superiorly beneath the inferior rectus.

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25
Q

What is orbitalis also known as and what is it?

A

Orbitalis (Müller’s muscle), a band of smooth muscle, covers the inferior orbital fissure.

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26
Q

What aperture is covered by the orbitalis muscle?

A

the inferior orbital fissure

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27
Q

What is shown in the diagram?

A

the orbit from in front with the globe removed to show the origins of the extraocular muscles and orbital nerves (vessels and fat not included in diagram)

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28
Q

What is shown in the image?

A

four views ot he right globe to demonstrate insertions of the extraocular muscles

IR: inferior rectus

SR: superior rectus

MR: medial rectus

LR: lateral rectus

SO: superior oblique

IO: inferior oblique

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29
Q

What is the innervation of the medial rectus muscle?

A

III (inferior)

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30
Q

What is the origin of the medial rectus muscle?

A

tendinous ring

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31
Q

What is the distance of the insertion of the medial rectus muscle from in mm from the cornea?

A

5.6mm

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32
Q

What is the tendon length of the medial rectus muscle?

A

3.6mm

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33
Q

What is the length of the muscle belly in mm of the medial rectus muscle?

A

40mm

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34
Q

What is the size of motor unit of the medial rectus muscle?

A

1:1.7 - 1:4

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35
Q

Which is the largest of the ocular muscles?

A

medial rectus muscle

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36
Q

What is the innervation of the inferior rectus muscle?

A

CN III (inferior branch)

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37
Q

What is the origin of the inferior rectus muscle?

A

tendinous ring

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38
Q

What is the distance of insertion of the inferior rectus muscle from the corna?

A

6.6mm

39
Q

What is the tendon length of the inferior rectus muscle?

A

5mm

40
Q

What is the muscle belly length of the inferior rectus muscle?

A

40mm

41
Q

What is the size of a motor unit of the inferior rectus muscle?

A

1:2 - 1:6

42
Q

What is the innervation of the lateral rectus muscle?

A

CN VI

43
Q

What is the origin of the lateral rectus muscle?

A

tendinous ring via two heads - opening between the two heads bridging the medial end of the superior orbital fissure

44
Q

What opening is bridged by the opening between the two heads of the lateral rectus muscle?

A

the medial end of the superior orbital fissure

45
Q

What is the insertion distance from the cornea of the lateral rectus muscle?

A

7.0mm

46
Q

What is the length of the tendon of the lateral rectus muscle?

A

8.4mm

47
Q

What is the length of the muscle belly of the lateral rectus muscle?

A

40mm

48
Q

What is the size of the motor unit of the lateral rectus muscle?

A

1:3 - 1:6

49
Q

What is the innervation of the superior rectus muscle?

A

CN III - superior branch

50
Q

What is the origin of the superior rectus muscle?

A

tendinous ring

51
Q

What is the distance from the cornea of the insertion of the superior rectus muscle?

A

7.8mm

52
Q

What is the tendon length of the superior rectus muscle?

A

5.4mm

53
Q

What is the length of the superior rectus muscle belly?

A

41mm

54
Q

What is the size of the motor unit of the superior rectus muscle?

A

1:4

55
Q

Where is the superior rectus muscle located in relation to other muscles?

A

lies beneath the levator palpebrae superioris

56
Q

What is the innervation of the superior oblique muscle?

A

CN IV trochlear nerve

57
Q

What is the origin of the superior oblique muscle?

A

superomedial to the optic canal

58
Q

What is the insertion of the superior oblique muscle?

A

lateral aspect of posterosuperior quadrant

59
Q

Describe the tendon of the superior oblique muscle?

A

tendon forms 10mm before winding around the trochlea

60
Q

What is the length of the muscle belly of the superior oblique muscle?

A

32mm

61
Q

What is the size of the motor unit of the superior oblique muscle?

A

1:5 - 1:6

62
Q

What is the only extraocular muscle with a fusiform shape?

A

superior oblique muscle

63
Q

Where does CNIV enter the superior oblique muscle?

A

on its upper border

64
Q

What is the innervation of the inferior oblique muscle?

A

CN III - inferior branch

65
Q

What is the origin of the inferior oblique muscle?

A

behind orbital margin lateral to nasolacrimal canal

66
Q

What is the insertion of the inferior oblique muscle?

A

posterolateral qudrant, mostly below horizontal

67
Q

Describe the tendon of the inferior oblique muscle.

A

very short tendon; muscle fibres almost reach the sclera

68
Q

What is the length of the muscle belly of the inferior oblique muscle?

A

34mm

69
Q

What is the size of the motor unit of the inferior oblique muscle?

A

1:7

70
Q

What is the only extraocular muscle not to originate at the apex of the orbit?

A

inferior oblique

71
Q

Where does the inferior oblique muscle pass?

A

between the eye and lateral rectus

72
Q

What are the 3 extraocular muscles innervated by the inferior division of the oculomotor nerve?

A
  1. medial rectus
  2. inferior rectus
  3. inferior oblique
73
Q

Which extraocular muscle is innervated by the superior division of the oculomotor nerve?

A

superior rectus

74
Q

What are 6 histological differences between extraocular muscle and skeletal muscle?

A

In the EOMs:

  1. Epimysium (muscle sheath) is very thin
  2. Fibres not tightly packed, separated by large amounts of connective tissue (perimysium)
  3. Fibres are rounded or oval with small fibres around periphery and large fibres in centre
  4. EOM is most vascular in the body (after myocardium)
  5. Normal EOM has changes normally associated with myopathy in other muscle
  6. Contains large numbers of specialised sensory/proprioreceptive endings
75
Q

What are 2 structures that are rich in the large amounts of connective tissue (perimysium) in extraocular muscles?

A
  1. reticulin
  2. elastic fibres
76
Q

What is the arrangement of muscle fibres by size in the EOM?

A
  • small fibres (5-15μm) are around the periphery of the muscle
  • larger fibres (10-40μm) in centre
77
Q

What is the most vascularised region of the extraocular muscles?

A

orbital aspect

78
Q

What are 5 histopathological/ultrastructural changes in normal EOM that are normally associated with myopathy?

A
  1. mild mononuclear cellular infiltrate
  2. centrally placed nuclei
  3. disorganisation of sarcolemma
  4. disruption of Z lines
  5. mitochondrial clumping
79
Q

What is an example of the specialised sensory/proprioreceptive endings contained in extraocular muscle? What are 3 examples of this?

A

large muscle spindles up to 1mm long:

  • nuclear bag fibres
  • nuclear chain fibres
  • annular nerve terminals
80
Q

How do the number of Golgi tendon organs differ in EOM?

A

found within the tendons of extraocular muscles in greater numbers than in skeletal muscle

81
Q

What is the course of afferent fibres from extraocular muscles?

A

initially in the cranial nerve innervating the muscle (III, IV or VI)

then leave these nerves and join ophthalmic division of the trigeminal (Va), either in cavernous sinus or the brainstem

82
Q

At what 2 points can afferent nerve fibres from the EOMs join the ophthalmic branch of the trigeminal nerve (Va)?

A

cavernous sinus or brainstem

83
Q

Where are the cell bodies of the afferent fibres of the EOMs situated? 2 locations

A
  1. mesencephalic nucleus
  2. some also traced to Purkinje cells in the cerebellum, play role in positional sense and control of ocular movements - saccadic and tracking
84
Q

What do the images show?

A

histological section of a) normal human skeletal muscle fibres and b) extraocular muscle fibres

85
Q

What is the likely reason for structural differences between EOM and skeletal muscle?

A

fundamental differences in function - constancy of activity (even during sleeping) and rapidity and fine gradation of contraction of EOMs required to fixate subjects of interest of fovea

86
Q

How many types of EOM muscle fibre hae been identified morphologically and how many functional types are there?

A
  • morphologically: 6 types
  • functionally: 3 types
87
Q

What are the 3 functional types of EOM fibres called?

A

type A, B and C

88
Q

What are 4 key differences between the 3 functional types of EOM muscle fibres?

A
  1. diameter of fibres
  2. end plates of fibres
  3. speed of muscle fibre twitch
  4. functional role - type of eye movements
89
Q

What are the relative diameters of muscle fibre types A-C?

A
  • A: large diameter
  • B: intermediate diameter
  • C: small diameter
90
Q

What are the relative number of end plates like for each type of EOM muscle fibre?

A
  • A: single end plate
  • B: multiple end plates
  • C: small en grappe plates
91
Q

What are the relative speeds of contraction of the different EOM muscle fibre types?

A
  • A: fast twitch
  • B: slow twitch
  • C: tonic contractions
92
Q

What type of eye movements are type A fibres required for?

A

saccadic movements

93
Q

What type of eye movements are type B fibres required for?

A

smooth pursuit movements

94
Q

What type of eye movements are type C fibres required for?

A

align both visual axes i.e. fine local contractions

ANATOMY3: Orbital contents (3 decks)

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